#include <bits/stdc++.h>

using namespace std;

struct ListNode
{
    int val;
    ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};

class Solution
{
public:
    ListNode *deleteDuplicates(ListNode *head)
    {
        if (head == nullptr)
        {
            return head;
        }
        ListNode *cur = head;
        while (cur)
        {
            ListNode *next = cur->next;
            while (next && next->val == cur->val)
            {
                next = next->next;
            }
            cur->next = next;
            cur = next;
        }
        return head;
    }
};